Stents or stent grafts are a form of transluminal prosthesis devices which are used to maintain, open or dilate stenotic lesions in body lumens which have been affected by disease. These prosthetic devices are typically either of two types including the balloon expandable and “self-expanding” varieties. Self expanding stents are inserted into the vascular system in a compressed or contracted state, are permitted to expand upon removal of a restraint typically referred to as a retractable sheath or sleeve. These stents are particularly advantageous for use because they may be formed of a shape memory alloy which is both resistant to compression and also has the ability to return to its previous shape. NITINOL is a shape memory alloy that is commonly used in stents and stent grafts. Alternative forms of self-expanding stents also exist which are not made of NITINOL such as the Wallstent® Endoprosthesis. In addition to metals, stents may also be formed of biodegradable materials.
It is often the case that a stenotic lesion occurs at a branch or bifurcation in a vessel. Placement and deployment of these prosthetic devices at bifurcations can be much more problematic. One current technique is to deploy a tubular stent having an opening across the bifurcation for placing a second stent through. Once the first stent is deployed, then the physician must then advance the second stent through the first stent.
It is advantageous in the case of bifurcations to utilize two separate guide wires to access the lesion and for positioning of each of the prosthetic devices used in the procedure including the second stent which is placed in the side branch.
This approach is advantageously used for positioning and deployment of balloon expandable stents. In the case of balloon expandable stents, the first stent, mounted on its delivery balloon is advanced over both the first guide wire and the second guide wire which exits from a hole in the mid-side portion of the stent and its balloon. This stent is then advanced to the first branch in the vessel at the region of the bifurcation and deployed. A second stent may then be advanced along the second guide wire through the hole in the first stent and positioned in the second branch at the region of the bifurcation. In this fashion, both stents may be accurately positioned and fixed in place by expansion of the balloon without the need to move either guide wire.
This approach is more problematic in the case of self-expandable stents because these stents are constrained in their form by a sheath, also referred to in the art as a sleeve or housing, which must be retracted in order to deploy the stent. Traditional sheaths are not formed with a hole to allow for exit of the side branch guide wire. Furthermore, even if such a hole was present, retraction of the sheath would be impossible in a two wire delivery system for self expanding stents.
One solution to this problem has been to add a slot from the wire exit port to the distal end of the sheath which allows the sheath to be retracted without moving the wire. Alternatively, a preferential tear line could be formed to make the slot. WO 99/34749 describes a self-expanding bifurcation stent and a delivery sleeve and method of delivery of such stents. The system includes a self-expanding stent and a corresponding delivery sleeve adapted to house two guide wires, one of which exits from the distal end and a second of which exits from a side hole in the stent. The preferred embodiments replace the hole with a longitudinal or oval slot. See WO 99/34749, pages 8-9. However, while the slot is advantageous for housing the second guide wire, keeping the sheath together is problematic. WO 99/34749 describes reinforcing the rim of the slot to adequately constrain the stent prior to deployment.
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